1. Field of the Invention
The invention relates to coatings for polycarbonate substrates and more particularly to optically clear, abrasion resistant, adherent coatings for polycarbonate lenses.
2. Description of the Prior Art
Polymeric ophthalmic lenses have become increasingly popular recently due to their fine optical properties, dimensional stability, impact resistance, light weight, etc. One serious disadvantage, nevertheless, to polymeric ophthalmic lenses, has been their susceptibility to scratching, particularly compared to traditional glass lenses. This is particularly true of polycarbonate lenses.
Much research has been devoted to providing coatings for polymeric lenses to improve their abrasion resistance. To date, however, none of the resultant coatings have proven totally successful as evidenced by their lack of commercial acceptance. This is probably because of the stringent requirements in optical and mechanical properties necessary in such coatings.
An example of one type of coating provided to solve this problem is given in U.S. Pat. No. 3,637,416 to Misch et al. The coatings described in the Misch et al. patent are applied by coating a plastic lens with a bonding or coupling film comprising an organic silicon compound and also coating it with a silica or silica gel. The preferred coating technique is a two-step technique, although both coatings can be applied simultaneously. Even in the one-step coating techinque, however, the combination of both an organic silicon compound and a silica or silica gel forming compound is present.
Still other attempts are described in U.S. Pat. No. 3,713,880 to Krekeler et al. The coatings described by this patentee contain alkyl silicates, trifunctional and/or bifunctional organosilanes and antistatic additives.
Many coating compositions designed for polycarbonate substrates are described in the patent literature. Examples of these include: evaporated vitreous mixtures of SiO and SiO.sub.2 in U.S. Pat. No. 3,811,753; silyl fluoroolefin polymers in U.S. Pat. No. 3,775,171; organosilanes in U.S. Pat. No. 3,713,880; evaporated layers of glass in U.S. Pat. No. 3,713,869; lightly cross-linked polyvinyl alcohol in U.S. Pat. No. 3,700,487; three layer composites of a hydroxylated polycarbonate, silica and poly(vinyl butyral), and silica and poly(vinyl alcohol) in U.S. Pat. No. 3,652,379; hydrophilic acrylate or methacrylate in U.S. Pat. No. 3,645,779; at least 50 successive vacuum deposited layers of SiO.sub.x in U.S. Pat. No. 3,552,080; hydrophilic acrylate or methacrylate in U.S. Pat. No. 3,488,215; SiO.sub.x coating formed by a glow-discharge oxygen-ion bombardment in U.S. Pat. No. 3,458,342; organopolysiloxane in U.S. Pat. No. 3,451,838 and U.S. Pat. No. 3,389,114; TEMA resins in U.S. Pat. No. 3,265,763; etc.
Despite the large amount of prior research, there is still a need for a process of forming adherent, abrasion resistant, optically clear coatings on polymeric ophthalmic components, and particularly on such components formed from polycarbonate.